student = {"zhangsan","lisi","wangwu","lisi"}
print(student)
if 'lisi' in student:
    print('lisi是一名学生')
else:
    print('lisi不是学生，不能进学校')

a = set('abcdef')
b = set('efghi')
print(a,b)
print(a-b)
print(a|b)
print(a&b)
print(a^b)